1. Field of the Invention
The present application relates to a multilayered film, a back sheet for a photovoltaic cell, methods of manufacturing the film and the back sheet, and a photovoltaic module including the film and the back sheet.
2. Discussion of Related Art
In recent years, there has been a growing interest in renewable energy and clean energy due to the earth's environmental problems and exhaustion of fossil fuels. Among these, solar light energy has attracted much attention as a representative pollution-free energy source that may solve issues in environmental pollution and exhaustion of fossil fuels.
A photovoltaic cell is a device configured to convert solar light into electric energy based on the principle of generation of electricity using solar light. Since the photovoltaic cell should be exposed to the outside for a long period of time to facilitate absorption of solar light, a unit, called a photovoltaic module, may be manufactured using various packaging processes for protecting the photovoltaic cell.
In general, a photovoltaic module may be manufactured using a back sheet having good weatherability and durability so that photovoltaic cells can be stably protected even if exposed to the outside for a long period of time. The back sheet may include a resin layer stacked on a substrate, and the resin layer may include a fluorine-based polymer, such as poly(vinyl fluoride) (PVF).
However, since the PVF resin is poorly adhesive to a polyethylene terephthalate (PET) film typically used as a substrate of a back sheet, an fluorine-based polymer film may be obtained using an extrusion or casting process and then laminated on the substrate using a urethane-based adhesive. In this case, however, high-priced film manufacturing equipment may be required, the use of an adhesive may be needed, and an adhesive coating process and a lamination process may be further performed. Furthermore, a film having a greater thickness than a required thickness may be adopted for convenience in handling the film during a film manufacturing process, the use of various additives and fillers may be limited, and a high process temperature may be required.
In another case, even if an fluorine-based polymer film is manufactured using a resin suspension or solution, coated on a substrate, and dried, since a solvent having a high boiling point is typically used, a high drying temperature of approximately 200° C. or higher may be required.
Since a PVF resin solution requiring a high drying temperature consumes a large amount of energy to provide a high drying temperature, the cost of manufacturing of a back sheet of a photovoltaic module may increase, thermal shock or thermal deformation may be caused to deteriorate the quality of products, such as mechanical properties of the products, and long-term use of the products outdoors may lead to rapid degradation in the mechanical properties of the products.
Therefore, there are ongoing demands for materials for a back sheet for a photovoltaic cell, which has good durability and weatherability, can be dried at a low temperature to reduce the cost of manufacturing of the back sheet for the photovoltaic cell, and can improve the productivity and quality of the photovoltaic cell.